Concept:
Polymers are very large molecules formed by the repeated linking of small molecules called monomers. In polymer chemistry, polymers are classified using certain standard parameters that help in understanding their origin, formation process, and molecular arrangement. The most common parameters used for classification of polymers are:
• Source of polymer
• Structure of polymer chain
• Mode of polymerization
• Molecular forces between polymer chains Physical properties of monomers such as boiling point are not used for classification.
Step 1: Classification based on source of polymer. Polymers are classified according to their origin as:
• Natural polymers – obtained from natural sources (e.g., cellulose, proteins, natural rubber)
• Semi-synthetic polymers – chemically modified natural polymers (e.g., cellulose acetate)
• Synthetic polymers – artificially synthesized in laboratories (e.g., nylon, polythene) Thus, source of polymer is an important classification parameter.
Step 2: Classification based on structure of polymer chain. Based on the arrangement of polymer chains, polymers are classified as:
• Linear polymers
• Branched polymers
• Cross-linked or network polymers Therefore, structure of polymer chain is also a valid classification parameter.
Step 3: Classification based on mode of polymerization. Polymers can also be classified according to the method by which monomers combine:
• Addition polymerization – monomers join without loss of small molecules
• Condensation polymerization – small molecules such as water or HCl are eliminated during polymer formation Hence, mode of polymerization is another classification parameter.
Step 4: Identify the incorrect parameter. The boiling point of a monomer is simply a physical property of the monomer molecule and does not influence the classification of polymers. Therefore, it is not used as a parameter for polymer classification.